Optical scanners for printing systems commonly employ some form of rotational drive mechanism for scanning a recording beam across an information storage device, such as a recording drum, planar medium, etc. Because the drive mechanism imparts rotational or oscillatory motion to the scanning optics, the rate of travel of the information beam across the recording medium is non-linear (typically sinusoidal), so that some form of image position correction must be introduced into the system. One approach has involved the use of a multifacetted rotating mirror or prism scanner having a constant speed drive in place of the sinusoidal scanner. Disadvantageously, the extremely high degree of precision to which each of the facets of the scanning optics must be ground and polished imparts an inordinate expense to such schemes; also wear of the moving parts of the constant speed drive creates a difficult alignment problem, making these systems practically unattractive.
Examples of such rotating polygon systems are described in the Swager U.S. Pat. No. 4,204,233 and Gilbreath U.S. Pat. No. 4,257,053. These patented systems propose to compensate for non-linearities by controlling the time of generation and modulation of the pixels based upon the non-linearities in the polygon facets. Such an approach is still akin to the costly and complex precision facet grinding and polishing techniques referenced-above, since highly refined analysis of the characteristics of each of the polygon's reflective surfaces is required.
Recognizing the complexity and cost shortcomings of the above proposals, there has been proposed a system described in the Broyles et al U.S. Pat. No. 4,037,231 which involves a simpler approach of addressing the non-linear (sinusoidal) movement of the scanning optics, and imparting a compensation into the modulations of the information beam. Unfortunately, this compensation involves only a segmented approximation of the non-linear travel of the sinusoidal scan and the non-linearities in the intensity of the pixel recording beam. As a result, the simplicity sought to be achieved by Broyles et al yields a system that suffers a loss in precision; also, it is not readily adaptable to a wide variety of scanning drive inputs. Moreover, in the system of Broyles et al the segmented approximation approach is implemented by incorporating separate control clocks for the different sinusoidal segments of interest, thereby involving additional circuit complexity. Of course, the accuracy of the Broyles et al approach is limited to within specified approximately linear regions or segments of the sinusoidal scan, thereby limiting the extent of coverage by the scanner.